Optical block with textured surface

ABSTRACT

An optical block includes a first surface that receives light entering the optical block, a second surface through which the light exits the optical block, and a reflector that reflects light from the first surface towards the second surface. The reflector includes a textured surface that scatters or absorbs some of the light received from the first surface to attenuate the light exiting the optical block through the second surface.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to optical blocks. More specifically, thepresent invention relates to an optical block with a modified surface.

2. Description of the Related Art

Good modulation characteristics of high-transfer-rate data includehaving high and uniform contrast between the “on” (digital 1) and “off”(digital 0) states. To achieve good modulation characteristics, it isoften necessary to operate a laser in an optical system that generatesthe high-transfer-rate data at a current well above the laser thresholdcurrent, which can generate an excessively large amount of lighttransmitted through an optical fiber. High optical power levels in anoptical fiber can cause detector saturation in a receiver and/or inducesignal distortion through optical nonlinearities. Thus, it is desirableto attenuate the amount of light before it enters the optical fiber.

To attenuate the light before entering into an optical fiber, it isknown to use an optical attenuator in the optical path of the light. Ifthe optical path includes an optical block, then it is known to use anoptical block made from different materials with different attenuationcharacteristics, e.g., 1 dB, 2 dB, etc. It is also known to use anin-line optical attenuator. For example, a thin-film on a glasssubstrate or a bulk absorptive attenuator can be used in the opticalpath. It is also known to defocus the light before it enters the opticalfiber. These techniques have the disadvantage that all channels musthave the same attenuation and cannot adapt to part-to-part variations.In addition, for bidirectional transceivers that include both transmitand receive channels in the same optical block, it can sometimes bedifficult with these techniques to only attenuate the transmitterchannels, which is desired so as to not reduce the sensitivity of thereceiver channels.

Adding an attenuator increases the part count and adds cost andcomplexity. Multichannel devices can require multiple attenuation blockswith different attenuation levels. Defocusing the light to decrease thecoupling into an optical fiber can result in the excitation ofundesirable cladding modes. Defocusing the light can increase themechanical adjustment range required to achieve the desired degree ofattenuation. If the optical fibers are arranged in an optical fiberribbon, then the attenuation of each optical fiber cannot beindividually adjusted because all the optical fibers are mechanicallylinked. Thus, there is a need for a method and apparatus that can reducethe transmitted light to an appropriate level without adding additionalcomponents or mechanical complexity and that can attenuate thetransmitted light on a channel-by-channel basis.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide an optical block that provides attenuation inan optical path, transmitter power monitoring, and variation in theattenuation between channels.

An optical block according to a preferred embodiment of the presentallows for the attenuation to be actively performed, while monitoringoptical power transmitted through an output optical fiber. A fraction ofthe transmitter power that is not coupled into the output optical fibercan be coupled into a photodetector, which can be used for transmitterpower monitoring. Transmitter power monitoring is useful in determiningthe operational status of the transmitter over its lifetime. Theattenuation can be customized for each channel in a multichannel device.

According to a preferred embodiment of the present invention, an opticalblock includes a first surface that receives light entering the opticalblock, a second surface through which the light exits the optical block,and a reflector that reflects light from the first surface towards thesecond surface. The reflector includes a textured surface that scattersor absorbs some of the light received from the first surface toattenuate the light exiting the optical block through the secondsurface.

The textured surface preferably includes at least one of dimples, dots,and scratches. The dots are preferably made of material with an index ofrefraction that matches or substantially matches an index of refractionof the optical block.

The optical block is preferably a molded optical block. Preferably, thetextured surface includes defects formed by a molding process or asurface modification process.

According to a preferred embodiment of the present invention, an opticalengine includes a substrate, a laser mounted to the substrate, anoptical block according to one of the various preferred embodiments ofthe present invention, and an optical fiber that receives light from thesecond surface of the optical block. The light received by the firstsurface of the optical block is generated by the laser.

The optical engine further preferably includes a photodetector thatdetects light scattered by the textured surface. The optical enginepreferably includes multiple channels. Preferably, at least two opticalchannels have different attenuation levels, or the textured surfacescatters the same amount of light for each channel of the multiplechannels.

According to a preferred embodiment of the present invention, a methodof attenuating light in an optical engine includes providing an opticalengine with a substrate; a laser mounted to the substrate; an opticalblock including a first surface that receives light entering the opticalblock from the laser, a second surface through which the light exits theoptical block, and a reflector that reflects light from the firstsurface towards the second surface; and an optical fiber that receiveslight from the second surface of the optical block; determining acurrent provided to the laser, measuring optical power in the opticalfiber, and texturing a surface of the reflector until the optical powermeasured in the optical fiber is reduced to a predetermined level toform a textured surface.

The textured surface preferably includes at least one of dimples, dots,and scratches. The dots are preferably made of material with an index ofrefraction that matches or substantially matches an index of refractionof the optical block.

The method further preferably includes molding the optical block. Thetextured surface preferably includes defects formed during the moldingof the optical block.

The textured surface is preferably formed from laser processing.Preferably, the laser is a pulsed laser and has an emission wavelengththat is absorbed in the optical block. The laser processing preferablyincludes scanning the laser across the reflective surface.

The above and other features, elements, characteristics, steps, andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of optical engine that can be used with thepreferred embodiments of the present invention.

FIG. 2 is a cross-sectional view that shows an optical path of theoptical engine shown in FIG. 1 .

FIG. 3 is a cross-sectional view of a portion of an optical engineaccording to a preferred embodiment of the present invention.

FIG. 4 is top view of a molded optical structure.

FIG. 5 shows a portion of a molded optical structure with a texturedarea on a reflector surface according to a preferred embodiment of thepresent invention.

FIG. 6 is a flowchart diagram showing a method of achieving the properattenuation level in all channels of an optical engine according to apreferred embodiment of the present invention.

FIG. 7 is a cross-sectional view of a portion of an optical engineaccording to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiments of the present invention can be used in anyapplication where the amount of optical power coupled into an opticalfiber needs to be attenuated by an adjustable amount, including, forexample, in an optical engine at an end of an active optical cable.

An optical engine is a device that performs optical-to-electricalconversion or electrical-to-optical conversion. For a receiver, theoptical engine provides optical-to-electrical conversion; for atransmitter, the optical engine provides electrical-to-opticalconversion; and for a transceiver, the optical engine provides bothoptical-to-electrical conversion and electrical-to-optical conversion.In a transceiver, the receiver and transmitter component are preferablyseparated to reduce cross-talk.

The optical engine typically includes electro-optical (EO) componentsconnected to a substrate. The optical engine can also include a moldedoptical structure (MOS) or optical block that connects to the substrateand to optical fibers of an optical cable. Instead of optical fibers,any suitable optical waveguide can be used. The MOS provides aninterface with the substrate at a position adjacent to the EOcomponents. Optical paths through the MOS between the EO components andthe optical fibers can include a lens system and a reflecting surface.The reflecting surface bends the light path, which can make aligning andmounting the optical fibers easier. The lens system controls the beamsizes, which can ensure good coupling efficiency between the variouselements in the optical path. The optical engine can include a pluralityof channels, each channel including an associated optical path. Theoptical engine can include a receive side and transmit side, and eachside can include a plurality of channels.

The optical engine can be used in numerous computer connector systemsincluding, for example: QSFP(+), CX4, CX12, SFP(+), XFP, CXP activeoptical cables; USB, CIO active optical cables; MDI, DVI, HDMI, DisplayPort, UDI active optical cables; PCIe x1, x4, x8, x16 active opticalcables; SAS, SATA, MiniSATA active optical cables.

FIG. 1 is an exploded view of a portion of optical engine 100, and FIG.2 shows an optical path 150 through the optical engine 100. FIGS. 1 and2 in this application are similar to FIGS. 2 and 7 in U.S. Pat. No.8,923,670, the entire contents of which are hereby incorporated hereinby reference. The optical engine 100 includes a substrate 102, EOcomponents 104 connected to the substrate 102, MOS 110 connected to thesubstrate 102, and optical fibers 112 connected to the MOS 110. Theoptical engine 100 is suitable for use with either single mode ormultimode optical fibers.

A channel is defined by a single path along which signals aretransported, i.e., transmitted and/or received. FIGS. 1 and 2 show achannel that includes an optical fiber 112, an optical path 150, an EOcomponent 104, and a trace 103. A transmitting channel includeselectrical signals that are inputted to the optical engine 100 at theedge of substrate 102, that propagate along the trace 103, that areconverted to optical signals in the EO component 104, and that continueto the optical fiber 112. A receiving channel includes optical signalsthat are inputted to the optical engine 100 at the optical fibers 112,that are converted to electrical signals in the EO component 104, andthat propagate along the trace 103 to the edge of the substrate 102.

The EO components 104 include, but are not limited to, laser diodes orlaser diode arrays for a transmitting channel and photodetectors orphotodetector arrays for receiving channels. The laser diode can produceeither a single- or multi-transverse-mode output beam. The laser diodeconverts an electrical current into light. A laser diode can be, forexample, a vertical-cavity surface-emitting laser (VCSEL), but otherelectrical-to-optical converters could also be used. The photodetectorconverts received light into a current. Any suitable photodetector canbe used. The EO components can be electrically connected to traces 103on the substrate 102 using either wire bonds or flip-chip techniques.

The MOS 110 is preferably connected to the substrate 102 at a positionadjacent the EO components 104. The MOS 110 includes a lens system 120that focuses and directs light from the optical fibers 112 onto the EOcomponents 104 and/or focuses and directs light from the EO components104 into the optical fibers 112. The MOS 110 can be made of a singleinjection-molded optical component or any other suitable device.

The MOS 110 includes grooves 114 that align and secure the opticalfibers 112 in the MOS 110. It is possible to use structures other thangrooves 114 to align the optical fibers 112. The grooves 114 can beV-shaped grooves or any other suitably shaped grooves. Each of thegrooves 114 receives and aligns a corresponding optical fiber 112 in theMOS 110. A pressure plate 130 secures the optical fibers 112 in thegrooves 114. The MOS 110 can include a strain-relief section 116 thatextends beyond the grooves 114. Epoxy 118 can be used to secure theoptical fibers 112 to the strain relief section 116. Grooves 114 allowassembly techniques in which the optical fibers 112 are held in a clampand stripped, cleaved, passively aligned, and permanently attached tothe MOS 110 in a single operation.

The MOS 110 can include one or more optical paths 150 through the MOS100. Each optical path 150 preferably includes a first lens 126positioned at a first end of the optical path 150 and a second lens 122positioned at a second end of the optical path 150. The first and secondlenses 122, 126 preferably collimate the light. The second lens 122 isadjacent to the optical fibers 112 and the first lens 126 is adjacent tothe EO components 104 but is not so limited. Each optical path 150further includes a reflector 124 positioned between the first lens 126and the second lens 122. The reflector 124 redirects light so theoptical path is bent. The bend in the optical path can be approximately90°, but this is not a requirement. The reflector 124 can use totalinternal reflection (TIR) to reflect all or substantially all of theincident light. The reflector can also use a reflective film applied tothe MOS 110. Using a reflective film eliminates the angular constraintsrequired of a TIR surface. Either or both of the first lens 126 or thesecond lens 122 can have no optical power, i.e. they are a flat surface.

Each optical path 150 includes a second section 151 and a first section152. The second section 151 includes a second lens 122 at a second endof the second section 151 and a reflector 124 at a first end of thesecond section 151. The second lens 122 can be adjacent to the opticalfibers 112, but is not so limited. The first section 152 includes thereflector 124 at a second end of the first section 152 and a first lens126 at a first end of the first section 152.

The MOS 110 can include a component cavity 162 that creates an enclosedspace between the planar surface of the substrate 102 and the MOS 110for the EO components 104 mounted on substrate 102.

The substrate 102 can be any suitable substrate, including, for example,an organic substrate (e.g., FR4) or a ceramic substrate (e.g., Alumina).The substrate 102 can include electrical traces 103 that are used toroute electrical data signals. The EO components 104 can include EOconverters, and the semiconductor chips 106 can include, for example,analog chips, that drive the EO converters. The semiconductor chips 106electrically drive the EO converters and can include, for example, alaser diode driver for the laser, and a trans-impedance amplifier (TIA)for the photodetector. The components of the optical engine 100 can besurface-mounted one the same side of the substrate 102 using standardsemiconductor assembly processes.

A riser 108 can be connected to the substrate 102. The riser 108, whichcan be formed from metallic or ceramic compositions, for example, servesas a planar mechanical reference for receiving and aligning the EOcomponents 104 and the MOS 110. The riser 108 is also used to conductheat generated by the EO components 104 and/or the semiconductor chips106 to one or more side or edge regions 109 of the optical engine 100.

The optical engine 100 can be manufactured using single-sided,surface-mount component assembly along with a two-step alignmentprocess. The EO components can be bonded on the substrate 102 relativeto fiducial marks by a precision die bonder. The EO components 104 forreceiving channels and transmitting channels can be aligned and bondedprecisely relatively to each other. The MOS 110 is aligned and bondedprecisely relatively to the EO components 104. The MOS 110 includesgrooves 114 for precise alignment of the optical fibers 112, and theoptical fibers 112 are passively placed in the grooves 114 and attachedto the MOS 110. In this manner, the optical fibers 112 are directlyattached and aligned to the MOS 110.

For transmitting channels, the electrical signal coming from theelectrical interface is preferably routed and wirebonded from thesubstrate 102 to a laser diode driver. The laser diode driver ispreferably wirebonded to the laser diodes. For receiving channels, theelectrical signal coming from the photodetector is preferably wirebondedto the TIA. The TIA is preferably wirebonded to the substrate 102 thatroute the electrical signals to the electrical interface. Thesecomponents can be mounted using any suitable technique, including beingflip-chip mounted.

Instead of or in addition to using an open cavity 160, the reflector 124can be modified to attenuate the amount of light that enters the opticalfiber 112. For example, the reflectivity of the reflector 124 can bereduced by defeating, spoiling, or degrading the surface of thereflector 124. Reduction of the surface reflectivity can be achieved byroughening, scratching, dimpling, or in some manner providing a finepitched mechanical texture to the surface of the reflector 124. Thetextured surface on the reflector 124 is generally formed only ontransmitting channels where attenuation of the optical power in theoptical fiber is desired. The reflector 124 on receiving channels canremain untextured.

FIG. 3 shows a cross-section of a portion of optical engine 100. A laser105 can be mounted on substrate 102. The laser 105 can be any suitablelaser including a VCSEL. The laser 105 can include one or moreindividual laser emitters. The laser 105 can provide a modulated opticalsignal suitable for very high bandwidth signal transfer down an opticalchannel. The laser 105 generates a light beam that follows the opticalpath 150. A first lens 126 can be provided on a surface of the MOS 110.The first lens 126 can collimate or focus the light emitted by the laser105. The reflector 124 preferably includes a textured surface so thatsome light is scattered or absorbed (scattered light is labeled as 111in FIG. 3 ) while some light is specularly reflected (reflected lightfollows the optical path 150) towards the optical fiber 112 (not shownin FIG. 3 ). The light can be reflected because of total internalreflection or an optical coating applied to the surface of the reflector124. A textured surface is defined as a surface with deliberately formeddefects that degrade the optical quality of the surface. Roughening asurface or applying a pattern of light absorbing or scattering dots arenon-limiting examples of forming a textured surface.

Optionally, a photodetector 107 can be mounted on the substrate 102 orsome other location. In FIG. 3 , alternative positions for thephotodetector 107 are shown on the substrate 102 and above the reflector124. But any suitable location can be chosen based on the spatialdistribution of the scattered light 111 by the textured surface of thereflector 124. Some of the scattered light 111 can be directed towardthe photodetector 107 such that the photodetector 107 samples a portionof the light emitted by the laser 105, which can be used fortransmission (TX) monitoring so that the laser power level can beverified and/or adjusted during operation of the optical engine 100. Thephotodetectors 107 can be used in transmitting channels with a laser 105as shown in FIG. 3 and can be used in receiving channels with aphotodetector. In a receiving channel, the photodetector 107 could be alower bandwidth, higher sensitivity photodetector that detects lowerspeed signals that the TIA does not output.

The MOS 110 can include features to isolate the individual channels fromeach other. For example, slits can be formed in the MOS 110 between thechannels and filled with a light absorbing material. The amount of lightreaching the photodetector 107 will be substantially proportional to theemitted laser power. It will also be substantially proportional to theoptical power transmitted through the optical fiber 112 because thefraction of scattered light from the reflector is independent of theincident power level.

FIG. 4 shows a top view of the MOS 110. The MOS 110 includes a reflector124 that directs light into an array of optical fibers 112. The MOS 110shown in FIG. 4 preferably includes twelve grooves 114 that can be usedwith twelve optical fibers 112 (not shown in FIG. 4 ), and thuspotentially twelve high-speed optical channels. FIG. 5 shows an exampleof a textured pattern on the surface of the reflector 124. The texturedpattern can be uniform or substantially uniform, within manufacturingtolerances, over the intersection region 113 where the optical path 150intersects with the surface of the reflector 124. The textured patterncan be an array of dimples 115 as shown in FIG. 5 . The dimples 115 canbe formed by laser marking or some other suitable method. The size ofthe dimples 115 in FIG. 5 has been exaggerated for clarity. Any numberof dimples 115 can be used. There can be tens, hundreds, or thousands ofdimples 115 on the surface of the reflector 124. The size and/or thenumber of dimples 115 can be adjusted to control the fraction ofscattered light 111. Increasing the number of dimples 115 and making thedimples 115 larger tends to increase the amount of scattered light 111.The dimples 115 can be formed in a regular array, or the dimples 115 canbe formed randomly to reduce possible patterns in the scattered light111 from interference effects.

The textured surface of the reflector 124 can be made using a lasermachining process, although other methods can be used. In the lasermachining process, a laser is directed and optionally focused on thesurface of the reflector 124. Application of the laser to the surface ofthe reflector 124 results in a spatially localized, mechanical,physical, or chemical alteration of the surface of the reflector 124.This alteration in the surface of the reflector 124 degrades thespecular reflectivity of the surface of the reflector 124. Preferably,the textured surface covers or substantially covers, withinmanufacturing tolerances, the intersection region 113. Covering theentire intersection region 113 allows a uniform or substantially uniformreduction in the specularly reflected light, without impacting itsspatial distribution. The coupling tolerances to the optical fiber 112are thus not impacted by the texturing; only the magnitude of thespecularly reflected light is impacted. It is also possible that thedesired level of attenuation can be reached by selectivity degrading thereflector 124 over only a portion of the intersection region 113.

The surface of the reflector 124 can be modified by any number ofmethods. For example, lasers can be used to locally modify thereflective properties of the surface of the reflector 124. Inparticular, lasers operating at ultraviolet wavelengths can be used.Pulsed lasers based on Q-switching or fiber amplifiers converted to UVwavelengths in the vicinity of 355 nm using nonlinear optical processesare an example of a class of lasers that can work well for thisapplication. Carbon dioxide lasers operating around 10 µm can also beuseful. Both the UV and 10-µm-wavelength lasers are strongly absorbed bythe optical quality plastic of the MOS 110. The pulse length of theselasers can be in the nanosecond or microsecond range, but this is not arequirement.

Alternatively, dots can be placed on the surface of the reflector 124.The dots can be absorptive, transparent, or translucent. The dots can bemade from a material with an index of refraction that matches orsubstantially matches the index of refraction of the MOS 110 such thatlight is transmitted with little or no reflection through the surface ofthe reflector 124 into the dot. The light can then be absorbed in thedot, scattered in the dot, or reflected and refracted off the dot’s rearsurface. Each of these mechanisms can attenuate the light coupled intothe optical fiber 112. The dots can be placed using ink-jet printingtechniques, but this is not a requirement.

Mechanical scribing or scratching of the surface of the reflector 124can also be used. For example, an array of sharpened pins can be pressedor dragged across the surface of the reflector 124. The array ofsharpened pins can be made using MEMS (Micro-Electronic MechanicalSystems) processing techniques, but this is not a requirement.

The surface of the reflector 124 can be modified during the moldingprocess of the MOS 110. That is, the MOS 110 can be molded such that thesurface of the reflector 124 includes spatially localized defects. Thesedefects can scatter light, reducing the amount of light that enters theoptical fiber 112. Using MOS 110 with prefabricated defects can reducethe number of defects that need to be fabricated in an active manner,thus reducing processing time.

It is possible that any optical surface, i.e., a surface either thatreflects light such as reflector 124 or through which light passes suchas lenses 122, 126, can be modified to adjust the attenuation to adesired level. It is also possible that more than one optical surfacecan be modified. It is also possible to modify optical surfaces thatinclude an optical coating. It is also possible to induce bulkscattering in the MOS 110 by creating spatially localized defects withinthe MOS 110. A focus laser with ultrashort pulses, i.e., picoseconds orfemtosecond pulse lengths, can be used to locally change the refractiveindex of the MOS 110, but this is not a requirement.

The localized modified regions can be referred to as spots, independentof how the spots are formed (laser, ink-jet, array of sharpened pins,molding, etc.). Spot sizes should be a small percentage of the overallbeam size. For example, if the optical path 150 provides a 200-µm beamsize on the surface of the reflector 124, then spot sizes less than 25µm are preferred. However, the spot size can be on the order of 1 µm, insome applications. Advantageously, a smaller spot size generally resultsin a more uniform attenuation of the light intensity. This makes thefraction of emitted light coupled into the optical fiber 112 independentof the spatial distribution of the emitted light. A further advantage ofsmall spot sizes is that it provides better resolution to control theamount of light coupled into the optical fiber 112. Many spots can bemade in a millisecond, and an array of spots can be made in less thanone second.

The amount of scattered light can be adjusted using the method shown inFIG. 6 . An optical engine 100 is first assembled. In step S101, theoptical engine can be mounted on an adjustment station. The adjustmentstation provides the capability to both drive a laser under test andmeasure the light transmitted from the optical fiber associated with thelaser under test. In step S102, a laser operating point can then bedetermined by finding a drive current that yields desirable modulationcharacteristics. As described above, this drive current can produce anexcessively large optical signal level in the optical fiber. In stepS103, the light in the optical fiber is measured. In step S104, thesignal level in the optical fiber can be decreased by texturing thesurface of the reflector. For example, the number of dimples, spots,defects, dots, or surface imperfections can be increased to increase theamount of scattered and/or absorbed light and reduce the amount of lightcoupled into the optical fiber. Alternatively, instead of, or inaddition to, increasing the number of defects, the size or roughness ofthe defects can be increased to increase the attenuation level. Forexample, a focused laser spot can be raster scanned over the reflectivesurface 124, and the optical power level in the optical fibers 112measured. If more attenuation is required, then the laser spot can beraster scanned over the same pattern, increasing the roughness of thereflective surface 124 and thereby increasing the attenuation level. Thetexturing can proceed until a desired fiber transmission level isachieved. In step S105, a determination is made as to if all of thechannels have been tested and had their respective optical power levelsin the optical fibers 112 adjusted. If all the channels have not beentested (the “No” decision in step S105), then in step S106 an untestedchannel is selected. If all the channels have been tested (the “Yes”decision in step S105), then in step S107, the optical engine is removedfrom the adjustment station.

It should be appreciated that the required attenuation can differbetween optical channels. In the preferred embodiments of the presentinvention, the attenuation level can be readily adjusted by changing thedegree of texturing for each channel. This is a significant advantageover the prior art technique of using a bulk attenuator having asubstantially uniform attenuation for all channels. In the preferredembodiments of the present invention, the desired attenuation in eachchannel can be achieved without adding an extra part, e.g., theattenuator, to the optical engine 100. The preferred embodiments of thepresent invention also can eliminate the need to stock a wide variety ofattenuators having different attenuation levels. Preferred embodimentsof the present invention can adjust the attenuation level to more than10 dB of the incident light. While any desired level of attenuation canbe achieved, typically attenuation levels are between 2 dB and 5 dB.Using small spots can provide an attenuation resolution of 0.01 dB ineach channel. But some applications may not require such fineresolution.

An optical surface with a textured surface can be combined with a bulkattenuator. The bulk attenuator provides a uniform attenuation level toall channels, and then each channel can be individually optimized bytexturing. This combined system has the advantage of reducing theattenuation range required from the textured surface.

While the preferred embodiments of the present invention have beendescribed in terms of a textured surface of an optical surface in anoptical engine, the concepts of the preferred embodiments of the presentinvention can be applied more broadly. For example, any optical datatransmission system requiring attenuation can use the techniquesdescribed above to attenuate an optical signal by modifying an opticalsurface in the optical path of the system. For example, rather than aMOS 110 transmitting light through the structure, an alternative MOS 210can be configured to reflect light from a first surface as shown in FIG.7 . The light path 150 never passes through the MOS 210. The reflectivesurface 124 could be curved to focus the light into the optical fiber112. The reflective surface 124 could be textured by focusing lightthrough the MOS 210 such that the focus is on or in the vicinity of thereflective surface 124. In this manner, the texturing light can modifythe reflective properties of the reflective surface 124 even though thereflective surface 124 is not on an external surface of the opticalengine 100. Any of the previously described texturing methods can alsobe used to provide the desired level of attenuation.

It should be understood that the foregoing description is onlyillustrative of the present invention. Various alternatives andmodifications can be devised by those skilled in the art withoutdeparting from the present invention. Accordingly, the present inventionis intended to embrace all such alternatives, modifications, andvariances that fall within the scope of the appended claims.

What is claimed is:
 1. An optical engine comprising: a substrate; alaser mounted to the substrate; an optical block including: multiplechannels; a first surface that receives light entering the optical blockthat is generated by the laser; a second surface through which the lightexits the optical block; and a reflector that reflects light from thefirst surface towards the second surface and that includes a texturedsurface that scatters or absorbs some of the light received from thefirst surface to attenuate the light exiting the optical block throughthe second surface; and an optical fiber that receives light from thesecond surface of the optical block.
 2. The optical engine of claim 1,wherein at least two channels have different attenuation levels.
 3. Theoptical engine of claim 1, wherein the textured surface scatters thesame amount of light for each channel of the multiple channels.
 4. Theoptical engine of claim 1, wherein attenuation levels of the multiplechannels of the optical engine are adjusted on a channel-by-channelbasis.
 5. A transceiver comprising: at least one transmit channel, eachat least one transmit channel includes an associated transmit opticalpath; and at least one receive channel, each of the at least one receivechannel includes an associated receive optical path; wherein at leastone associated transmit optical path includes deliberately formeddefects configured to attenuate light propagating in the at least onetransmit optical path; and no associated receive optical path includesdeliberately formed defects configured to attenuate light.
 6. Thetransceiver of claim 5, further comprising an optical block, wherein thedeliberately formed defects are on a surface of the optical block. 7.The transceiver of claim 5, wherein the at least one transmit channel isa plurality of transmit channels.
 8. The transceiver of claim 7, whereinat least two of the plurality of transmit channels include differentattenuation levels.
 9. A transmitter comprising: a plurality of transmitchannels, each of the plurality of transmit channels includes anassociated transmit optical path; wherein at least two associatedtransmit optical paths include deliberately formed defects configured toattenuate light propagating in the at least two associated transmitoptical paths, and the at least two associated transmit optical pathshave different attenuation levels.
 10. The transmitter of claim 9,further comprising an optical block, wherein the deliberately formeddefects are on a surface of the optical block.
 11. A method of reducinga light level in an optical fiber, the method comprising: providingmultiple data transmission channels; forming defects in a reflectivesurface; generating light; and reflecting the light off the reflectivesurface prior to the light entering the optical fiber; wherein thedefects in the reflective surface reduce the light level in the opticalfiber.
 12. The method of claim 11, further comprising individuallyoptimizing the light level in each of the multiple data transmissionchannels.